One thing that bothered me w.r.t. to the earlier thread on penetration was the anecdotal evidence that light carbons penetrate better on targets than do heavier, and higher momentum, aluminums. I think that Joe Tapley, homepage.ntlworld.com/joetapley/target.htm, has the answer.

He shows that targets slow arrows primarily by grabbing the shaft. For this kind of a force, penetration does relate to KE - not momentum. Plus carbon arrows have a smaller diameter such that the force slowing them down is less than the force slowing down an aluminum arrow. So, for most commercial targets, extra momentum is little advantage and larger diameter is a big disadvantage.

For a deer, on the other hand, the broadhead cuts a hole for the shaft. The forces slowing down the arrow traveling through the deer are viscous forces - like a boat plowing through water - and cutting forces. For both of these the forces are proportional to velocity and the penetration is directly proportional to momentum.

Bottom line, as usual, no free lunch - those targets are lieing to us!

beprepn